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Eustachian Tube and Internal Carotid Artery in Skull Base Surgery: An Anatomical Study

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The Laryngoscope VC 2014 The American Laryngological, Rhinological and Otological Society, Inc. Eustachian Tube and Internal Carotid Artery in Skull Base Surgery: An Anatomical Study Jianfeng Liu, MD,
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The Laryngoscope VC 2014 The American Laryngological, Rhinological and Otological Society, Inc. Eustachian Tube and Internal Carotid Artery in Skull Base Surgery: An Anatomical Study Jianfeng Liu, MD, PhD; Carlos D. Pinheiro-Neto, MD, PhD; Juan C. Fernandez-Miranda, MD; Carl H. Snyderman, MD, MBA; Paul A. Gardner, MD; Barry E. Hirsch, MD; Eric Wang, MD Objectives/Hypothesis: The eustachian tube (ET) is an important landmark in skull base surgery, which has a close relationship with the petrous segment of the internal carotid artery (ICA). The goal of the current study was to establish the detailed anatomic relationship of the ET and petrous segment of the ICA. Study Design: Anatomical study. Methods: Six silicon-injected adult cadaveric heads (12 sides) were dissected using a lateral infratemporal fossa approach (type C) and endoscopic endonasal approach. The ET and ICA were exposed; their detailed relationships were demonstrated. High-quality pictures were obtained. Results: In the anterior genu/foramen lacerum segment of the ICA, the vidian nerve was an important landmark. The cartilaginous ET was divided into four segments, from anterior to posterior: nasopharyngeal, pterygoid, lacerum, and petrosal segment. The anterior and inferior wall of the carotid canal was consistently between the horizontal ICA and petrous segment of the cartilaginous ET. In the posterior genu of the ICA, the bony part of the ET, and the tendon of the tensor tympani muscle were paramount landmarks. The posterior genu of the ICA was imbedded in the carotid canal. The landmarks of the junction of the cartilaginous ET and bony ET were the sphenoid spine and foramen spinosum. Conclusions: The anatomical segmentation of the ET provides the basis for safe and effective transection of the ET in skull base surgery. An understanding of the complex relationships of the ET and petrous segment of the ICA is paramount for surgically dealing with disease located within the region of the ET and petrous segment of the ICA. Key Words: Eustachian tube, internal carotid artery, petrous segment, endoscopic, skull base surgery. Level of Evidence: NA Laryngoscope, 124: , 2014 INTRODUCTION The most critical structure in lateral skull base surgery is the petrous segment of the internal carotid artery (ICA). Just after the artery enters the carotid canal (CC), the short vertical ascending segment turns at the level of the cochlea. This turn of the ICA corresponds to the posterior genu. Then the artery courses anteriorly and medially toward the foramen lacerum. Just above to the fibrous tissue of the foramen lacerum, the petrous ICA curves superiorly to continue as the paraclival ICA. The second curve is called the anterior genu of the ICA and has a close relation with the foramen lacerum. Considering the course of the ICA within Additional Supporting Information may be found in the online version of this article. From the Department of Otolaryngology (J.L., C.D.P.-N., C.H.S., B.E.H., E.W.) and Department of Neurosurgery (J.C.F.-M., C.H.S., P.A.G., B.E.H.), University of Pittsburgh Medical Center, Pittsburgh, Pennsylvania; and the Department of Otolaryngology (J.L.), China-Japan Friendship Hospital, Beijing, China. Editor s Note: This Manuscript was accepted for publication June 10, The authors have no funding, financial relationships, or conflicts of interest to disclose. Send correspondence to Juan C. Fernandez-Miranda, MD, Department of Neurological Surgery, Suite B-400, Presbyterian University Hospital, 200 Lothrop Street, Pittsburgh, PA DOI: /lary the temporal bone, the petrous carotid can be anatomically divided into four segments: vertical, posterior genu, horizontal, and anterior genu. 1 The eustachian tube (ET) is an important landmark in skull base surgery, and has a close spatial relation with the petrous segment of the ICA. 2 4 Despite few publications about the relationship of the ET and the ICA, 5 7 the literature is lacking a profound anatomical description of this complex area. Comprehensive anatomical knowledge is paramount to achieve efficiency and safety during endoscopic endonasal approaches in this region. The goal of this study was to describe in detail and correlate the anatomical relationship of the ET and the petrous segment of the ICA from two different approaches: open microscopic and endoscopic endonasal. MATERIALS AND METHODS Six adult cadaveric heads (12 sides) were dissected. The specimens were previously injected with colored silicone. In three heads (six sides), a lateral infratemporal approach type C was performed. In the remaining three heads (six sides), an endoscopic endonasal approach to the petrous segment of the ICA was done. The ET and ICA were exposed in both approaches. High-quality photographs were produced. Infratemporal Fossa Approach Type C The skin incision was C-shaped above and posterior to the lateral orbital margin. Transection and closure of the external auditory canal were completed. After exposing the facial nerve 2655 Fig. 1. Microscopic views of related bony structures of the eustachian tube (ET) and carotid canal (CC). (A) The extracranial surface of the middle skull base focusing on the ET- and CC-related bony structures. Inferolateral view of the ET- and CC-related bony structures in the right side. The CC passes within the petrosa, initially upward, and then inward and forward to the foramen lacerum. The ET sulcus runs parallel to the CC. (B) Close view of the ET- and CC-related bony structures in the right side from the anterior-medial perspective. The semicanal of the tensor tympani muscle and semicanal of the ET are anterior-lateral to the carotid foramen. The anterior end of the ET sulcus is close to the foramen lacerum medially and scaphoid fossa laterally. Lateral to the ET sulcus are the sphenoid spine, foramen spinosum, and foramen ovale, respectively, from posterior to anterior. (C) Anteromedial view of the right-side petrous part of the temporal bone. The internal orifice of the CC opens at the petrous apex. The semicanal of the tensor tympanic muscle, semicanal of the ET, hiatus for the greater superficial petrosal nerve, and trigeminal impression are shown. (D) Posterolateral view of the sphenoid bone. The internal carotid artery passes above the fibrocartilage of foramen lacerum after leaving the petrous apex then courses in the carotid groove of the sphenoid bone. The vidian canal is inferolateral to the beginning site of the carotid groove. Ant. 5 anterior; Canal. 5 canaliculus; Car. 5 carotid; Chiasm. 5 chiasmatic; Clin. 5 clinoid; Cochl. 5 cochlear; Cond. 5 condyle; Fiss. 5 fissure; For. 5 foramen; Gr. 5 greater; Impre. 5 impression; Infratemp. 5 infratemporal; Int. 5 internal; Jug. 5 jugular; Lat. 5 lateral; M. 5 muscle; Mandib. 5 mandibular; Med. 5 medial; Occip. 5 occipital; Orb. 5 orbital; Ori. 5 orifice; Pet. 5 petrosal; Petrotymp. 5 petrotympanic; Proc. 5 process; Pteryg. 5 pterygoid; Pterygopalat. 5 pterygopalatine; Sphen. 5 sphenoid; Sup. 5 superior; Super. 5 superficial; Tens. 5 tensor; Trige. 5 trigeminal; Tub. 5 tubal; Tuberc. 5 tubercle; Tymp. 5 tympanic/tympani. in the parotid, the zygomatic arch was exposed and dissected 360 o from the surrounding musculature and soft tissue. Two osteotomies were performed in the zygomatic arch. Then the arch was removed to allow adequate inferior retraction of the temporalis muscle. The temporalis muscle was elevated and retracted inferior to expose the bony roof of the infratemporal fossa. Subtotal petrosectomy was performed. After identification of the vertical ICA, a retractor was used to expose the infratemporal fossa with exposure of the mandibular condyle and the mandibular fossa. Subperiosteal dissection was carried out to expose the base of the middle cranial fossa and the lateral pterygoid process. Further access to the infratemporal fossa was obtained by drilling the bone at the base of the middle cranial fossa. The middle meningeal artery, mandibular nerve (V3), and ET were identified. The ICA was followed toward the foramen lacerum. The pterygoid muscles were cut. The ET was followed toward its pharyngeal opening. The periosteum of the petrous apex and clivus was sharply elevated. Scissors were used to cut the fibrous attachments at the level of the petro-occipital fissure 8,9 (see Supporting Information, Fig. 1, in the online version of this article). Endoscopic Endonasal Approach Three heads (six sides) were used to perform endoscopic dissection with rod-lens endoscopes, 4 mm in diameter, 18 cm in length, and with 0 o and 45 o lenses (Storz Endoscopy, Tuttlingen, Germany). The Image 1 system (Storz Endoscopy), with a highdefinition video camera, enabled video images of the endoscopic anatomy to be recorded during the study. Endoscopic skull base surgical instruments (Storz Endoscopy), and skull base surgical drills and navigation (Stryker Corp, Kalamazoo, MI) were used to complete the dissection. This study was performed through endonasal combined with Caldwell-Luc approaches, and transmaxillary, transpterygoid, transinfratemporal fossa, and transpetrous approaches to expose the ET and ICA. In addition, 2656 Fig. 2. Lateral and anterior views of the eustachian tube (ET) and its related structures. (A) Lateral view of the ET from the middle ear cavity to the nasopharynx in the right side. Petrosectomy has been performed; the ET has been exposed after removing external structures in the infratemporal fossa. The lateral walls of the semicanal of the ET and semicanal of the tensor tympani muscle have been drilled, and the lumen of the ET has been opened to show the whole course of the ET from the tympanic orifice to the nasopharyngeal orifice. (B) Endoscopic endonasal view of the ET and related structures in the left side. The ET passes from the middle ear cavity lateral superiorly to the nasopharynx medial inferiorly. The posterior genu of the internal carotid artery (ICA) runs beneath the bony ET. The walls of the cartilaginous portion are supported chiefly by the cartilage in the form of medical lamina and lateral lamina, completed laterally and inferiorly, by a membranous lamina of connective tissue. A. 5 artery; Cart. 5 cartilaginous/cartilage; Chor. 5 chorda; For. 5 foramen; Gang. 5 ganglion; Gen. 5 geniculate; Gr. 5 greater; Int. 5 internal; Jug. 5 jugular; Lat. 5 lateral; M. 5 muscle; Mandib. 5 mandibular; Max. 5 maxillary; Mem. 5 membranous; N. 5 nerve; Paraph. 5 parapharyngeal; Proc. 5 process; Pteryg. 5 pterygoid; Pterygopala. 5 pterygopalatine; Rosenm. 5 Rosenm uller; Seg. 5 segment; Semicirc. 5 semicircular; Sphen. 5 sphenoid; Tens. 5 tensor; Tub. 5 tubarius; Tymp. 5 tympani/tympanic; V. 5 vein; V2, maxillary nerve; V3, mandibular nerve. antrostomy, ethmoidectomy, sphenoidotomy, orbital decompression, skeletoning of the lateral wall of the sphenoid sinus, and resection of the medial maxillary wall were performed. Under visualization with a 0 o endoscope, the dissection was started with bilateral resection of the middle turbinate and complete sphenoethmoidectomy. A posterior septectomy was carried out to join both sphenoid sinuses. The floor of the sphenoid sinus was drilled up to the level of its posterior wall providing a broad communication between the sphenoid sinus and the nasopharynx. The nasopharyngeal aperture of the ET was well appreciated. A medial maxillectomy was performed to widely expose the posterior wall of the maxillary sinus from the nasal floor to the orbit. To facilitate the dissection in the infratemporal fossa, a Caldwell-Luc approach was added. Using both routes (transnasal and transmaxillary), the dissection was connected with the approach to the infratemporal fossa contents. Then, a complete transpterygoid approach was performed. The drilling of the petrous part of the temporal bone was continued to the petrous segment of the ICA (see Supporting Information, Fig. 2 and Fig. 3, in the online version of this article). RESULTS ET- and Carotid Canal-Related Bony Structures The ICA enters the cranial cavity through the CC located in the petrous part of the temporal bone. The CC passes within the petrous bone, initially upward and then inward, and forward to the foramen lacerum (Fig. 1A,B). There are three segments to the CC: vertical, bend (genu), and horizontal (Fig. 1B) (see Supporting Information, Fig. 4, in the online version of this article). The carotid foramen is medial to the vaginal process of the tympanic bone, anterior to the jugular foramen (Fig. 1A,B). Anterolateral to the carotid foramen there are two small canals, called the semicanal of the tensor tympani muscle and the semicanal of the ET, which pass under the tubal process of the tympanic portion attached to the petrous (see Supporting Information, Fig. 4A,B in the online version of this article). Anterior-medial to the semicanals, anterior and parallel to the horizontal segment of the CC, is the bony bed for the cartilaginous portion of the ET termed the ET sulcus (Fig. 1A,B). The anterior end of the ET sulcus is adjacent to the foramen lacerum medially and scaphoid fossa laterally (Fig. 1A,B). At the foramen lacerum, the ET and ICA are separated by fibrocartilaginous layers. The ET runs from the ET sulcus to the nasopharynx through the scaphoid fossa. Lateral to the ET sulcus are the sphenoid spine, foramen spinosum, and foramen ovale, respectively, from posterior to anterior (Fig. 1A,B). The foramen lacerum is bounded posteriorly by the petrous apex, anteriorly by the base of the medial pterygoid plate, and posteromedially by the basioccipital bone (Fig. 1A,B). The internal orifice of the CC opens into the superior portion of the foramen lacerum turning anteromedially to reach the carotid groove (Fig. 1C,D). Anatomy of the ET The ET extends from the tympanic ostium on the anterior and inferior wall of the tympanic cavity inferiorly to reach the lateral wall of the nasopharynx. It passes inferiorly, anteriorly, and medially (Fig. 2). In the 2657 Fig. 3. Lateral microscopic views of the anterior genu of the internal carotid artery (ICA) and cartilaginous eustachian tube (ET) in the right side. (A) The vidian nerve is a landmark of the anterior genu of the ICA, which situates anteroinferolateral to the genu. The base of the vidian nerve is encased by the fibrocartilaginous tissue around the foramen lacerum. The lateral wall of the ET has been severed to expose the lumen of the ET. The course of the ET has been shown. The cartilaginous ET is divided into four segments including the petrous, lacerum, pterygoid, and nasopharyngeal segments. (B) The vertical part, posterior genu, and horizontal part of the petrous segment, anterior genu, and posterior vertical part of the cavernous sinus segment of the ICA have been exposed. The bony ET has been removed; the course of the petrous ICA and the course of the ET have been shown. (C) The cartilaginous ET has been divided and resected from the sulcus of the ET anterolaterally, foramen lacerum fibrocartilage anteromedially, and pharyngobasilar fascia inferiorly. It has been retracted anteriorly. The nasopharyngeal cavity is opened. The petrous part inferior to the ICA and medial to the cartilaginous ET has been exposed. (D) The lateral clivus and petroclival fissure have been exposed. The rough and thick fibrocartilaginous tissue of foramen lacerum is inferior to the anterior genu of ICA, which continues with the petroclival fissure fibrocartilage posterolaterally, cartilaginous ET anterolaterally, and pharyngobasilar fascia anteromedially. A. 5 artery; Ant. 5 anterior; Ca. 5 canal; Cart. 5 cartilage/cartilaginous; Cond. 5 condyle; For. 5 foramen; Gang. 5 ganglion; Gen. 5 geniculate; Gr. 5 greater; Hori. 5 horizontal; Mandib. 5 mandibular; Med. 5 medial; Mid. 5 middle; N. 5 nerve; Nasopha. 5 nasopharyngeal; Pet. 5 petrosal; Pharyngobas. 5 pharyngobasilar; Post. 5 posterior; Pteryg. 5 pterygoid; Seg. 5 segment; Semicirc. 5 semicircular; Sphen. 5 sphenoid; Super. 5 superficial; Tymp. 5 tympanic; V3, mandibular nerve; Vert. 5 vertical lateral one-third of its length, it has a bony wall that constitutes the semicanal; in the medial two-thirds the wall is cartilaginous (Figs. 2 and 3). The bony part begins at the tympanic ostium on the anterior and inferior wall of the tympanic cavity and ends at the isthmus (Fig. 1B,D) (see Supporting Information, Fig. 4A, in the online version of this article). The irregularly triangular bony lumen gradually contracts toward the jagged anteromedial extremity; this is the narrowest point in the entire auditory tube and is named the isthmus, which is the junction of the squamous and petrous portions of the temporal bone (Fig. 1B,C and Fig. 2), and lies just medial to the sphenoid spine (Fig. 1B,C). The cartilaginous part is formed by a triangular plate of cartilage. It widens as it progress from the isthmus toward the lateral wall of the nasopharynx. The nasopharyngeal opening of the ET is situated just posterior to the inferior nasal concha and in front of Rosenm uller recess. The posterior lip of the pharyngeal orifice is the mobile portion of the ET, which forms the torus tubarius (Fig. 2). The walls of the cartilaginous portion are formed chiefly by the tubal cartilage, which contributes to the medial lamina and the narrower lateral lamina. Inferiorly and laterally, a membranous layer of connective tissue joins both laminas and completes the lumen wall of the cartilaginous ET (Fig. 2, Fig. 3B,D). Anatomical Segments of the ET The ET has been traditionally divided into cartilaginous and bony portions. From a surgical point of view, this classification is not sufficient. According to its anatomical relationship with surrounding structures, the cartilaginous ET can be divided into four segments from Fig. 4. Endoscopic endonasal view of the anterior genu of internal carotid artery (ICA) and cartilaginous eustachian tube (ET). (A) The 0 o endoscopic view of the cartilaginous ET and foramen lacerum fibrocartilage, paraclival, parasellar segments of the ICA, and the important landmark, the vidian nerve (VN) and artery. The cartilaginous ET is divided into four segments: petrous, foramen lacerum, pterygoid, and nasopharyngeal. (B) A 45 o endoscopic view of the relationships of the anterior genu of the ICA, foramen lacerum cartilage, pharyngobasilar fascia, and different segments of the cartilaginous ET and VN. (C) A 0 o close view of the cartilaginous ET, base of the VN, and foramen lacerum cartilage. The base of the VN and artery indicates the anteroinferolateral wall of the foramen lacerum. Under the base of the VN, the petrous segment of the cartilaginous ET passes within the sulcus of the ET. The cartilaginous ET has been separated from the anterior end of the medial wall of the sulcus of ET, which is the inferolateral wall of the carotid canal. (D) The ET has been divided and retracted inferiorly. The relationship of foramen lacerum fibrocartilage, pharyngobasilar fascia, and petroclival fissure fibrocartilage is illustrated. The dense fibrocartilaginous tissue of foramen lacerum is inferior to the anterior genu of the ICA, which continues with petroclival fissure cartilage posterolaterally, cartilaginous ET anterolaterally, and pharyngobasilar fascia anteromedially. A. 5 artery; Ant. 5 anterior; Cap. 5 capitis; Car. 5 carotid; Cart. 5 cartilage/cartilaginous; Fiss. 5 fissure; For. 5 foramen; Fos. 5 fossa; Gr. 5 greater; Hori. 5 horizontal; Inf. 5 inferior; Lac. 5 lacerum; Lat. 5 lateral; Long. 5 longus; M. 5 muscle; Mem. 5 membranous; N. 5 nerve; Nasoph. 5 nasopharyngeal; Paracl. 5 paraclival; Paraph. 5 parapharyngeal; Parase. 5 parasellar; Pet. 5 petrosal; Petrocl. 5 petroclival; Pharyngobas. 5 pharygobasilar; Post. 5 posterior; Pteryg. 5 ptergoid; Seg. 5 segment; Sphen. 5 sphenoid; Super. 5 superficial; V2, maxillary nerve; V3, mandibular nerve. posterior to anterior: petrous, lacerum, pterygoid, and nasopharyngeal segments (Fig. 1B, Fig. 3A, Fig. 4A C, Fi
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